import math

a=0.5
b=4
error=0.001
delta=0.001

times=math.ceil(math.log((b-a)/error,2))



def fun(x):
    return x*math.log(x)-1

#times=1
def d2(a,b,times):
    if times==0 or b-a<=delta:
        return (a+b)/2
    mid=(a+b)/2
    if fun(mid)>0:
        return d2(a,mid,times-1)
    elif fun(mid)<0:
        return d2(mid,b,times-1)
    else:
        return mid


print("%.3f"%d2(a,b,times))